This invention relates to a semiconductor differential amplifier and a method of protecting the amplifier against undesirable effects of transitional power events.
Integrated circuits based on semiconductor manufacturing process are well known. Such devices are understood to be formed by providing a suitable base and then forming electrical circuit components on the substrate. Such devices are understood to be formed with many such components on a single substrate, with such components functioning as transistors, resistors and other elements. Input/output (I/O) controllers, as one example only, are so formed and have components of the types described formed on the substrates supporting the components. This technology is well known and needs no further description here.
Many such integrated circuit devices or chips use as one type of component a differential amplifier. Differential amplifiers have been long recognized in the art, to the extent that there exist entire texts devoted to the characteristics and design of such amplifiers and their inclusion in large scale integrated circuits. The interested reader is referred to such texts for a deeper understanding of the invention here to be described.
Differential amplifiers function due to the imposition of voltages there across, and serve, among other purposes, to amplify the differences between two input voltages (hence the name) and to remove noise otherwise present in signals by operating in so-called common mode. One difficulty encountered with integrated circuits formed by the use of certain technologies is that voltages may be applied across a differential amplifier which result in either signal distortion beyond acceptable limits or damage to the components forming the amplifier. This is particularly true where an Integrated Circuit (IC) chip is made by a technology which is only capable of offering thin oxide transistors with limited maximum voltage tolerance and the element is used in a circumstance where compliance with communication protocol standards requires handling voltages which may, in transition, exceed desirable levels. Even if thick oxide devices are available in a given technology, and might be less susceptible to voltage problems, those devices are often incapable of the speed necessary to support the applications in question.
As device geometries shrink, the maximum supported power supply voltage also decreases. While this allows digital technology to have a higher maximum operating speed, IC I/O must continue to meet minimum output amplitude as dictated by communication standards. Achieving large output amplitudes often requires higher power supply voltages which, when imposed across a minimum geometry device, impair longevity.